Disposable toothbrush having mint flavored toothpaste composition bonded to bristles thereof

ABSTRACT

A flavored toothpaste composition is bonded to the bristles of a disposable toothbrush by a process which involves the chemical grafting and polymerizing of selected monomers and prepolymers to the bristles via a free radical mechanism. This process locks in the flavor until the product can be utilized. When the toothpaste is brought into contact with an aqueous medium, such as saliva in the oral cavity, the toothpaste dissolves thereby releasing the desired flavor to the teeth and oral cavity.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent Ser. No. 08/742,462,filed Nov. 1, 1996; now U.S. Pat. No. 5,783,249, which is a divisionalof Ser. No. 08/409,909, filed Mar. 23, 1995, now U.S. Pat. No.5,605,736, which is a continuation of Ser. No. 08/150,599, filed Nov.10, 1993, now abandoned, which is a continuation-in-part of Ser. No.08/121,161, filed Sep. 14, 1993, now abandoned.

BACKGROUND OF THE INVENTION

To accommodate the busy and often harried traveler, disposabletoothbrushes have been designed that can be used away from home, forexample on a trip, or that can be offered for single use inestablishments receiving the public, such as hotels and restaurants.These disposable toothbrushes have eliminated the need for a separatetube of toothpaste by incorporating in or on the brush a sufficient doseof a flavored toothpaste for brushing the teeth, the flavor being addedto encourage oral hygiene practices. Many such crior art disposabletoothbrushes are complex and/or expensive, as where a mechanism isincluded for distributing the toothpaste onto the bristles just prior touse. In other prior art disposable toothbrushes, the toothpaste ispreapplied to the bristles, but such toothbrushes have proved unstable,in that the flavoring dissipates after a relatively short period oftime, which is impractical as commercial considerations require areasonable shelf life. As a result, prior art disposable toothbrusheshave, for the most part, not proved commercially successful, primarilybecause no known prior art disposable toothbrush has satisfied themultiple criteria of a preapplied toothpaste thereby eliminating theneed for a distribution mechanism, a reasonable shelf life, and a lowmanufacturing cost. Regarding manufacturing costs, it is well known thatservice establishments, such as hotels, will not provide to theirpatrons disposable items which exceed a preestablished cost.

Hospitals, of course, also provide toothbrushes to their patients.Typically, hospitals provide a toothbrush and a separate tube oftoothpaste, the tube typically including sufficient toothpaste for alimited number of uses. This, however, poses two problems. First, thereis a risk of transmission of infectious disease, as when a patientplaces his/her toothbrush on a sink, etc. Secondly, in the case of apatient having use of only one arm, as is sometimes the case whenpatients are treated intravenously, it is difficult for the patient tomanipulate the toothpaste onto the bristles of the toothbrush.

For the foregoing reasons, there is a need for an individually wrapped,inexpensive disposable toothbrush having a toothpaste compositiondistributed over the bristles of the toothbrush and in which theflavoring does not dissipate over a reasonable shelf life.

OBJECTS AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a flavoredtoothpaste composition bonded to a toothbrush, wherein the flavor isstabilized and long-lasting.

It is a further object of the invention to provide a disposabletoothbrush which is coated with an amount of toothpaste sufficient for asingle tooth brushing operation such that the toothbrush may be disposedof after initial use.

It is another object of the invention to provide a method of manufactureof a disposable toothbrush and toothpaste product with a long-lasting,stabilized flavor.

It is still another object of the invention to provide a disposabletoothbrush and toothpaste product that can be produced at low cost.

It is yet another object of the invention to provide a disposabletoothbrush that is both safe and convenient to use, e.g., in a hospitalsetting.

The present invention is thus directed to a disposable toothbrush andtoothpaste product obtained by a process which involves the chemicalgrafting and polymerization of selected monomers and prepolymers to thebristles of the toothbrush. More particularly, the process of thepresent invention comprises the steps of contacting the bristles of thetoothbrush (in general hereinafter being referred to as "the substrate")with a composition containing a ferrous salt as the graft initiator, amonomer/prepolymer, and a catalyst which activates polymerization by theferrous ion, whereby the ferrous ions are reduced by the substrate withfree radicals being formed as a result on the substrate. Themonomer/prepolymer attaches itself to these free radical sites, thusforming an intimate covalent bond with the substrate. The toothbrushcontaining the toothpaste composition is then dried to complete thegraft bonding of the toothpaste to the substrate.

The strength of the resulting bond can be adjusted so that the flavoredtoothpaste is immediately activated when brought into contact withnormal mouth fluids, i.e., water and saliva, and is released by thescrubbing action of the bristles against the teeth, imparting adesirable flavor to the teeth and mouth of the user thereof.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS Mechanism ofChemical Grafting

A. As Applied to Natural and Polymeric Substrates

Chemical grafting involves activation of a substrate. Once the substratehas been activated, chains of monomers linked by carbon-carbon bondsgrow on the substrate, bonding to the substrate without damaging any ofthe existing positive characteristics of the materials involved. Manymaterials, both naturally occurring and synthetic, possess activehydrogens which are more reactive than the "bulk hydrogens," thetertiary hydrogen in polypropylene for example.

Thus, graft initiators (G.I.) have the capacity of removing these activehydrogens and concomitantly initiating the growth of polymer chains atthe site from where the active hydrogen was removed. In the case ofpolypropylene, this can be represented as follows: ##STR1##

In this illustration, (°) can represent either a free radical, anion orcation, depending on whether the G.I. removes a hydrogen and oneelectron, no electrons or two electrons, respectively. CH₂ ═CHxrepresents a unit of vinyl monomer where "x" governs the property orproperties obtained. In many instances a mixture of monomers is employedand often more than one property can be altered in one processing step.These polymer chains, whose length can be controlled, are stronglyattached to the substrate. The linkage between the graft polymer and thesubstrate is covalent in nature, and therefore, the graft polymer cannotbe leached from the substrate. In essence, chemical grafting is a matterof growing polymer chains on the backbone chain of a substrate. Thegraft polymer chains are formed from vinyl monomers or monomerscontaining appropriate functionality, e.g., groups such as hydroxyl,carboxyl, epoxy, amide, amine, anhydride.

B. Chemical Grafting as Applied to a Nylon, Polypropylene or PolyesterSubstrate of a Toothbrush

In the case of a nylon, polypropylene or polyester substrate, such as atoothbrush bristle, the chemical grafting is carried out via theabstraction of the hydrogen atom from the --CONH-- group (nylon),##STR2## with the graft initiator to form a free radical which thenreacts with a monomer/prepolymer solution, by which graft polymerizationcommences. The sequence of reaction steps involved in the chemicalattachment of the monomer/prepolymer onto the toothbrush substrate isbelieved to take place as follows: ##STR3## The graft polymerizationshown in steps (1)-(4) may be terminated by radical combination whichmay occur as: ##STR4## The foregoing reactions take place in thepresence of a peroxide which concurrently regenerates the graftinitiator forming a free radical as shown in reaction step (4). ##STR5##Reaction (1) provides a radical site on an exemplary substrate (S-H) bythe reduction of the graft initiator and oxidation of the substrate totransform the substrate into a free radical. Reaction (2) illustratesthe grafting of an exemplary monomer to the activated substrate (S°) atthe free radical site to form a graft polymer radical on the substrate.This is followed by propagation in reaction (3). Reaction (4)illustrates the formation of a menthol radical, e.g.; from a peppermintcompound. Reaction (5) illustrates chain termination via combination ofthe menthol radical with the activated substrate graft polymer formed instep (3), the end result being the chemical attachment of a monomer mintprepolymer to the surface of the toothbrush bristles. Reaction (6)illustrates the regeneration of the graft initiator ion by the presenceof peroxide in the monomer solution.

Method of Preparation of the Mint-Flavored Toothpaste Formulation

The present invention is directed to a polymeric toothpaste compositionthat is chemically grafted to the bristles of a toothbrush to form astrong adhesion to the bristles over an extended period of time. Aspreviously stated, chemical grafting involves the use ofmonomers/prepolymers, a catalyst, and a graft initiator along with otherexcipients in the composition.

The monomers and prepolymers are vinyl monomers and acrylic and vinylprepolymers which chemically bond to the bristles via a Free radicalsystem. The monomers and prepolymers are preferably acrylic monomershaving one or more hydroxyl and carboxyl groups. Some of the monomersand prepolymers of this type are the following: polyvinyl alcohol,acrylic acid, polyacrylic acid, methacrylic acid, ethyl acrylate, ethylmethacrylate, isobutylmethacrylate, and methyl acrylate. Also, mixturesof two or more monomers can be used. Polyvinyl alcohol, acrylic acid andpolyacrylic acid are preferred.

The formulation is prepared by taking the ingredients in the order asindicated in the examples or any other convenient order.

Ferrous ions are preferred as graft initiators for the grafting ofdesired monomers/prepolymers onto the bristles, but other metal ionssuch as Ag ions could also be used or any other metal ion which is safefor mouth application.

The presence of a small amount of a peroxide catalyst, preferablyhydrogen peroxide, helps to regenerate the graft initiator system in theprocess which in turn provides free radicals for further chain graftpolymerization. Other representative peroxides include peracetic acidand urea peroxide.

The amounts of the reactants employed is not a critical feature of theinvention. For obvious economical reasons, the amounts ofmonomer/prepolymer, graft initiator and catalyst employed in the systemwill be the minimum amounts necessary to complete the reaction aspreviously described herein. The amounts of monomer and prepolymeremployed will normally range from about 0.0001% to about 2% by weight ofthe composition, though the preferred concentration ranges from about0.0001% to about 0.2% by weight. The amount of graft initiator rangesfrom about 0.00001% to about 0.01% by weight, preferably from about0.00001% to about 0.001%. The amount of peroxide catalyst employed willnormally range from about 0.001% to about 1% by weight, preferably fromabout 0.001% to about 0.5%.

Suitable materials for use as flavors are those which allow the user todetect a strong, noticeable flavor while permitting maintenance of anacceptable product appearance. The flavors may be of natural orsynthetic origin. Such flavors include peppermint, spearmint,wintergreen, cinnamon, and the like; fruit flavors such as cherry,strawberry, lime, and the like. Preferred flavors for use in toothpasteinclude peppermint and spearmint.

Examples of auxiliary excipients utilized in the present inventioninclude fillers, surfactants, buffers and pigments.

The formulation described herein has several advantages. First, iteliminates the need for a complex and expensive article that is intendedto be used only once. Second, it eliminates, when traveling, the needfor packing both a toothbrush and a tube of toothpaste. And finally, theintimate bond that is formed when the toothpaste is applied to thebristles locks in the freshness and flavor for a long period of time.

In the preferred embodiment of the invention, the bristles of thetoothbrush are dipped into a toothpaste that contains monomers,prepolymers, graft initiator ions, peroxide ions and other excipients ofthe composition. The coated samples are then air dried at roomtemperature for approximately 30 to 40 minutes, whereby the hydroxyl andcarboxyl groups from the monomers/prepolymers in the toothpastepolymerize to form a strong adhesion to the bristles of the toothbrush.

Where the toothpaste is applied to the bristles as a single coat, theformulation consists basically of the monomer/prepolymer, catalyst,graft initiator, pigment, flavoring and other auxiliary excipients. Thedesired amounts of each filler, namely calcium carbonate, sodiumhydrogen carbonate, sodium lauryl sulfate, potassium tripolyphosphateand sodium fluoride are combined in a container and mixed until ahomogeneous mixture is obtained. Likewise the desired amounts of themonomer/prepolymer, graft initiator and pigment are combined in acontainer and stirred until the solution is uniform. The mixture offillers is then added in small increments with continuous stirring tothe uniform solution. The polyacrylic acid is then added, followed bythe mint flavored compound, and the contents are blended to a smoothpaste. The hydrogen peroxide is finally added and the paste is mixedagain until uniform. The prepared reactive formulation may then beapplied to the toothbrush by dipping the toothbrush into the toothpasteand then, if necessary, the product may be exposed to air drying for 30to 40 minutes to complete the graft bonding. If desired, the dryingprocess may be accelerated by subjecting the product to heat, e.g., at atemperature of about 212° F. to 300° F. for 1 to 2 minutes.

The following examples illustrate formulations which may be used in theinvention.

EXAMPLE

    ______________________________________    Composition             Parts by Weight    ______________________________________    1.   Calcium carbonate      500.00    2.   Sodium hydrogen carbonate                                20.00    3.   Sodium lauryl sulfate  15.00    4.   Potassium tripolyphosphate                                2.50    5.   Sodium fluoride        1.00    6.   Glycerol (solvent)     250.00    7.   Acrylic acid, 0.1% in glycerol (monomer)                                0.10    8.   Graphtol green 5884-2 (pigment)                                0.10    9.   Ferrous ammonium sulfate, 0.1% solution                                0.01         (Items 6, 7, 8 and 9 are blended together         as a premix.)    10.  Polyacrylic acid, 1% solution                                0.10         (prepolymer)    11.  Peppermint oil         20.00    12.  Hydrogen peroxide, 0.1% solution                                0.01    ______________________________________

Ingredients 1-5 (all solids) were blended together until a uniform mixwas obtained. This mixture was then poured with continuous stirring tothe glycerol premix of ingredients 6-9 and the resulting blend mixedagain to a uniform paste. The polyacrylic acid was then added, followedby the peppermint oil, and the paste blended until smooth. Hydrogenperoxide was added and the paste was mixed again, the resulting pastebeing ready for use.

The bristle part of the toothbrush was dipped directly into thetoothpaste and lifted up. The amount of paste on the brush was adjustedby controlling the depth the bristles sink into the paste. The paste wasthen air dried.

EXAMPLE

    ______________________________________    Composition             Parts by Weight    ______________________________________    1.   Calcium carbonate      500.00    2.   Sodium hydrogen carbonate                                20.00    3.   Sodium lauryl sulfate  15.00    4.   Potassium tripolyphosphate                                2.50    5.   Sodium fluoride        1.00    6.   Glycerol               250.00    7.   Acrylic acid, 0.1% in glycerol                                0.10    8.   Graphtol green 585H-2  0.10    9.   Ferrous ammonium sulfate, 0.1% solution                                0.01         (Items 6, 7, 8 and 9 are blended together         as a premix.)    10.  Polyacrylic acid, 1% solution                                0.10    11.  Spearmint oil          20.00    12.  Hydrogen peroxide, 0.1% solution                                0.01    ______________________________________

The formulation in example 2 was made exactly the same as in Example 1,the only difference being that spearmint oil was substituted for thepeppermint oil. The paste was applied to the brush also by the samemethod.

EXAMPLE

    ______________________________________    Composition             Parts by Weight    ______________________________________    1.   Calcium carbonate      500.00    2.   Sodium hydrogen carbonate                                20.00    3.   Sodium lauryl sulfate  15.00    4.   Potassium tripolyphosphate                                2.50    5.   Sodium fluoride        1.00    6.   Glycerol               250.00    7.   Acrylic acid, 0.1% in glycerol                                0.10    8.   Graphtol green 5884-2  0.10    9.   Ferrous ammonium sulfate, 0.1% solution                                0.01         (Items 6, 7, 8 and 9 are blended         together as a premix.)    10.  Polyacrylic acid, 1% solution                                0.10    11.  Peppermint oil         20.00    12.  Hydrogen peroxide, 0.1% solution                                0.01    13.  Deionized water        80.90    ______________________________________

Example 3 was made exactly as Example 1 but after the first 12ingredients were blended, water was slowly added with continuous mixing,the resulting mix blended to a smooth consistency. The bristles weredipped into the formulation and allowed to dry.

EXAMPLE

    ______________________________________    Composition             Parts by Weight    ______________________________________    1.   Calcium carbonate      500.00    2.   Sodium hydrogen carbonate                                20.00    3.   Sodium lauryl sulfate  15.00    4.   Potassium tripolyphosphate                                2.50    5.   Sodium fluoride        1.00    6.   Glycerol               250.00    7.   Acrylic acid, 0.1% in glycerol                                0.10    8.   Graphtol green 5854-2  0.10    9.   Ferrous ammonium sulfate, 0.1% solution                                0.01         (Items 6, 7, 8 and 9 are blended together         as a premix.)    10.  Polyacrylic acid, 1% solution                                0.10    11.  Spearmint oil          20.00    12.  Hydrogen peroxide, 0.1% solution                                0.01    13.  Deionized water        80.90    ______________________________________

Example 4 was made the same way as Example 3 except for the substitutionof spearmint oil for peppermint oil. The bristles were dipped into thepaste and were ready for packing when dry.

Where the toothpaste is applied to the bristles in two coats, the primecoat consists basically of the flavoring and the prepolymer, whereas thetop coat consists of the monomer, catalyst, graft initiator, pigment andother auxiliary excipients. The desired amount of flavor is mixed withthe prepolymer and applied to the bristles by dipping, then curing at200° F. for 4-5 minutes. The desired amounts of each filler, namelycalcium carbonate, sodium hydrogen carbonate, sodium lauryl sulfate andpotassium tripolyphosphate are combined in a container and mixed until auniform mix is obtained. A solution of the pigment is prepared, added tothe uniform mix, and mixed until a uniform blend is obtained. Thedesired amounts of the monomer, graft initiator and catalyst are thenadded to the blend and the contents are mixed well. The preparedformulation may then be applied as a top coat over the prime coat bydipping the already flavor-treated toothbrush into the top coat andcuring at 300° F. for 2 minutes.

The following example illustrates a formulation which may be used in theinvention.

EXAMPLE

    ______________________________________    Composition             Parts by Weight    ______________________________________         Prime Application    1.   Polyvinyl alcohol 523  200.00         8% solution in water    2.   Peppermint (polarome)  30.00         Top Application    3.   Calcium carbonate      1000.00    4.   Sodium hydrogen carbonate                                50.00    5.   Sodium lauryl sulfate  34.00    6.   Potassium tripolyphosphate                                5.00    7.   Deionized water        162.00    8.   Mx 439 PYLA-Cert Green 0.20    9.   Glycerol               500.00    10.  Acrylic acid, 0.1% in glycerol                                0.20    11.  Ferrous ammonium sulfate, 0.1% solution                                0.02    12.  Hydrogen peroxide, 0.1% solution                                0.02    ______________________________________

Ingredient 1 was prepared by adding small increments of polyvinylalcohol to deionized water with continuous stirring until all particleswere wetted out. The solution was heated to 185° F.-205° F. (85° C.-96°C.) for 30 minutes and then allowed to cool to room temperature. Thepeppermint was then added to this solution, mixed and applied as a primecoat to the bristles by dipping. The product was then cured at 200° F.for 4-5 minutes. Next, ingredients 3, 4, 5 and 6 were blended togetheruntil a uniform mix was obtained (Part A). Ingredients 7 and 8 weremixed well, ingredient 9 was added, and the contents mixed again (PartB). Part B was then mixed into Part A until a uniform blend was obtained(Part C). Ingredients 10, 11 and 12 were then added to Part C and mixedwell for 1-2 minutes. The formulation thus prepared was ready to use asa top coat over the prime coat containing the flavor. This top coat wasapplied to the already treated bristles by dipping. The product was thencured at 300° F. for 2 minutes.

It should be understood that the preferred embodiments and examplesdescribed are for illustrative purposes only and are not to be construedas limiting the scope of the present invention which is properlydelineated only in the appended claims.

What is claimed is:
 1. A method of bonding a flavored toothpastecomposition to a substrate, comprising the steps of:(a) providing atoothbrush having bristles comprising said substrate; (b) activating thesubstrate with a graft initiator; (c) bonding a monomer/prepolymer tothe activated substrate; (d) polymerizing the monomer/prepolymer to forma graft polymer chain; (e) chemically bonding a flavoring to the polymerchain, steps (b) through (e) being performed in the presence of acatalyst; and (f) drying the toothbrush containing the flavoredtoothpaste composition to complete the graft polymerization whereby theflavoring is preserved until the toothbrush and flavored toothpastecomposition is utilized.
 2. The method of claim 1, wherein said step (a)comprises providing a toothbrush having bristles containing in theirmolecular structure active hydrogens for graft polymerization at vacatedhydrogen sites.
 3. The method of claim 1, wherein said step (a)comprises providing a toothbrush having nylon, polypropylene orpolyester bristles.
 4. The method of claim 1, wherein said step (b)comprises activating the substrate with a graft initiator in the form ofmetal ions for abstracting active hydrogens and transforming theabstracted sites into free radical sites to which the monomer/prepolymerattaches, the result being a covalent bond of the monomer/prepolymer tothe toothbrush bristles.
 5. The method of claim 4 wherein said step (b)comprises activating the substrate with a graft initiator in the form offerrous ions.
 6. The method of claim 1, wherein step (b) furthercomprises reduction of the graft initiator and oxidation of thesubstrate so as to form a free radical in the substrate.
 7. The methodof claim 1, wherein step (c) further comprises grafting themonomer/prepolymer to the activated substrate to form a graft polymerradical on the substrate.
 8. The method of claim 1, wherein step (d)further comprises growing polymer chains on the substrate.
 9. The methodof claim 1, wherein step (e) further comprises the steps of:(i) forminga menthol radical; and (ii) combining the menthol radical with theactivated substrate graft/polymer formed in step (d), the result being acovalent bonding of the flavoring to the surface of the toothbrushbristles.
 10. The method of claim 1, further comprising the step ofcuring the toothbrush containing the flavored toothpaste composition ata temperature of about 212° F. to about 300° F. for about 1 to 2minutes.
 11. The method of claim 1, wherein said step (e) compriseschemically bonding a flavoring to the polymer chain in the presence of aperoxide catalyst.
 12. The method of claim 11, wherein said step (e)comprises chemically bonding a flavoring to the polymer chain in thepresence of hydrogen peroxide.
 13. The method of claim 1, wherein saidstep (c) comprises bonding acrylic acid and polyacrylic acid to theactivated substrate.
 14. A method of bonding a flavored toothpastecomposition to a substrate, the substrate being the bristles of atoothbrush, comprising the steps of:(a) applying a single coat of thetoothpaste composition to the bristles of the toothbrush, the singlecoat including a monomer/prepolymer, a catalyst, a graft initiator,flavoring and other auxiliary excipients; and (b) air drying thetoothbrush containing the flavored toothpaste composition.
 15. Themethod of claim 14, wherein the single coat further comprises a pigment.16. The method of claim 14, wherein said step (a) comprises:(i)activating the substrate with the graft initiator; (ii) bonding themonomer/prepolymer to the activated substrate; (iii) polymerizing themonomer/prepolymer to form a graft polymer chain; and (iv) chemicallybonding the flavoring to the polymer chain, (i) through (iv) beingperformed in the presence of the catalyst.
 17. The method of claim 14,wherein said step (a) comprises applying a single coat including a graftinitiator in the form of metal ions for abstracting active hydrogens andtransforming the abstracted sites into free radical sites to which themonomer/prepolymer attaches, the result being a covalent bond of themonomer/prepolymer to the toothbrush bristles.
 18. The method of claim17, wherein said step (a) comprises applying a single coat including agraft initiator in the form of ferrous ions.
 19. The method of claim 17,wherein the single coat also includes a pigment.
 20. The method of claim18, wherein the single coat also includes a pigment.
 21. The method ofclaim 15, wherein (i) further comprises reduction of the graft initiatorand oxidation of the bristles to transform the bristles into a freeradical.
 22. The method of claim 16, wherein (ii) further comprisesgrafting the prepolymer to the activated substrate to form a graftprepolymer radical on the substrate.
 23. The method of claim 16, wherein(iii) further comprises growing polymer chains on the substrate.
 24. Themethod of claim 16, wherein (iv) further comprises:(a) forming a mentholradical; and (b) combining the menthol radical with the activated graftprepolymer substrate formed in (ii), the result being a covalent bondingof the flavoring to the surface of the toothbrush bristles.
 25. Themethod of claim 14, wherein step (b) is conducted at room temperaturefor about 30 to 40 minutes.
 26. The method of claim 14, furthercomprising the optional step (c) of curing the toothbrush containing theflavored toothpaste composition.
 27. The method of claim 26, whereinstep (c) is conducted at a temperature of about 212° F. to 300° F. forabout one to two minutes.
 28. The method of claim 14, wherein said step(a) comprises applying a single coat including a peroxide catalyst. 29.The method of claim 28 wherein said step (a) comprises applying a singlecoat including a hydrogen peroxide catalyst.
 30. The method of claim 16,wherein (i) through (iv) are performed in the presence of a peroxidecatalyst.
 31. The method of claim 30, wherein (i) through (iv) areperformed in the presence of a hydrogen peroxide catalyst.
 32. Themethod of claim 14, wherein said step (a) comprises applying a singlecoat including an acrylic acid monomer and a polyacrylic acidprepolymer.